1. Field of the Invention
This invention relates to the packaging of integrated circuit dies. More particularly, this invention relates to an improved structure and method for packaging integrated circuit dies which incorporates advantages of both ceramic and plastic packaging.
2. Description of the Related Art
Conventionally, integrated circuit dies or chips have been packaged either in hermetically sealed ceramic containment structures or by encapsulating the die in plastic. While the hermetically sealed ceramic structure provides an excellent packaging of the integrated circuit die, it is an expensive construction, since the hermetic seal must be of sufficient quality so that moisture and other contaminants cannot penetrate into the package and damage the integrated circuit die therein.
The difficulties and expense encountered in providing a ceramic package with an adequate hermetic seal have, in the past, led those skilled in the art to utilize plastic packaging materials instead, which are used to encapsulate the integrated circuit die. By first attaching the die physically and electrically to a lead frame and then completely surrounding the die with plastic, the die was effectively sealed from contaminants as long as high quality plastic encapsulation material was used.
However, the use of plastic-encapsulated packaging has not been without its problems. In the first place, the die (and the portions of the lead frame immediately adjacent the die) are conventionally encapsulated in plastic by inserting the die and lead frame into a mold in a plastic injection press and plastic material is then injected under high pressure into the mold. To prevent the injected plastic from escaping from the mold via the spaces in between the individual leads on the lead frame, dams of removable metals are usually placed between the leads. These dams are then subsequently removed after the encapsulation step. However, since the injected plastic terminates at one side of the dams, removal of the dams without damage to the integrated circuit package, including the plastic encapsulant, requires special tools and the exercise of considerable care.
The encapsulation of the die in plastic requires the injection of such plastic under pressure. This, in turn, necessitated the use of short and stiff bonding wires between the leads of the lead frame and the contacts on the integrated circuit die. Longer leads could be bent, under the pressure of the injected plastic, to short against adjacent bonding wires. Furthermore, bonding wires which were not sufficiently thick would not possess the requisite stiffness to inhibit either bending or breakage of the bonding wire induced by the pressure of the injected plastic.
Heat dissipation is also not as satisfactory using plastic encapsulation since ceramic materials are better heat conductors. Thus, the use of plastic encapsulation has resulted in the need for employment of metal heat sinks and/or the use of central die paddles in the metal lead frame to assist in conducting the heat away from the die during operation of the integrated circuit die.
The use of a die paddle or other suitable die support means is also necessitated in plastic encapsulation type packaging to properly position the integrated circuit die or chip centrally in the injection mold, prior to encapsulation, to make sure that the die will be completely surrounded by the encapsulating plastic material.
In view of all these problems associated with plastic-encapsulated circuit die packaging, it would be highly desirable to provide a packaging structure and method wherein the low cost advantages of plastic packaging could be realized while overcoming the problems normally encountered with plastic packaging, in contrast to packaging utilizing ceramic materials.